Portable electronic device users have shown increasing interest in biometric tracking Biometric sensors often need to be in close or even direct contact with the skin to properly measure and track biometric parameters along the lines of heart rate, VO2, and core temperature. Requiring a user to place a sensor in direct contact with the skin to track these types of biometric data can be overly burdensome, making adoption of the biometric tracking more difficult. Consequently, mechanisms for unobtrusively measuring biometric parameters are desirable.